Several stirring devices for molten metal have been introduced previously. The Japanese Patent Kokai No. 52-153802 describes the structure of a stirring device in which a stirring tube penetrates through the upper part of a side wall of a melting furnace at an inclination ranging from 25 to 60 degrees. The stirring tube is fixed against the wall. The Japanese Patent Kokai No. 58-185730 describes a structure in which a riser tube is connected to an opening in the lower part of a side wall of a melting furnace.
These devices are, however, designed with fixed stirring tubes which present various troubles in its operating process. Regarding the structure of Japanese Patent Kokai No. 52-153802, solid metal charges collide with the stirring tube to damage the tip of the tube, and the high speed hot stream of the melting metal degrades the durability of the stirring tube. Furthermore, the protrusion of the stirring tube into the melting furnace hinders efficient skimming operations. For the structure of Japanese Patent Kokai No. 58-185730, the repeated melt discharge operations promotes the deposition of scum at the inlet of the opening connected to the riser tube, which then blocks the opening and results in the shut down of furnace operation.
To resolve these problems, the inventors of this invention previously presented an improved stirring device which is described in detail in Japanese Utility Model Kokai No. 63-95099. In the improved device, a stirring tube passes through an insertion hole in the side wall of a furnace, then the stirring tube is angled using a tilting device to allow the tip of the stirring tube dip into the molten metal. This improved device, however, has no positioning mechanism to move the stirring tube along the axis of the stirring tube, so that the dipping position of the stirring tube cannot be changed and adjusted to a position to obtain the best stirring efficiency in case the depth of molten metal changes in the melting furnace. In addition, since the improved device is provided with a stationary structure to mount the stirring device next to a melting furnace, every melting furnace required its own exclusive stirring device. For factories operating more than one melting furnace, this pairing of furnace and stirring equipment raises the costs of plant investment and hinders efficient use of space. Another remaining problem concerned the function of stirring tube insertion adjustment to respond to the various types of furnace wall shapes or to the scum conditions inside the furnace.